Continuous casting method with degassed glass-like blanket



May 9, 1967 CONTINUOUS CASTING METHOD WITH DEGASSED GLASS-LIKE BLANKET Filed March 18, 1965 lNl/E/V TOR NORM/7N f? 6055 A5) M041;

United States Patent 3,318,363 CONTINUOUS CASTING METHQI') WITH DEGASSED GLASS-LIKE BLANKET Norman P. Goss, Mentor, Ohio, assignor to Oglebay Norton Company, Cleveland, Ohio, a corporation of Delaware Filed Mar. 18, 1965, Ser. No. 449,726) 6 Claims. (Cl. 164-82) This invention relates to an improvement in the continuous casting of metal utilizing a degassed blanket of glass-like or molten salt material on top of the metal in the mold, which blanket is of a consistency to pass downwardly into the air gap between the congealing metal and the walls of the mold so as to lubricate the passage of the metal downwardly through the mold.

While the problem herein presented will be discussed specifically in connection with the continuous casting of steel, it should be understood that this invention has uses with other metals and steel is discussed here because it is a condition of great difiiculty when casting this metal. The advantages of a blanket of glass-like or molten salt material at the top of the metal level in a continuous casting mold having a vertical passageway are many. The congealing metal in the mold shrinks away from the cool mold wall leaving an air gap of varying thickness. The blanket of glass-like or molten salt material on top of the molten pool in the mold keeps slag and other solid particles out of the air gap; it keeps the friction between the congealing metal and the mold walls at a minimum; it improves the heat transfer from the congealing metal to the cool mold walls and the plastic glass-like or molten salt material is self-accommodating to variations in the air gap; it prevents wear on the mold walls; decreases re checking of the walls; keeps the metal evenly heated in the top of the mold thus aiding flow of the metal particularly where the mold section is of large area; follows the changing metal level in the mold with varying teeming rates; prevents excessive chilling of the metal upon first entering the mold; prevents splashes of the metal sticking to the mold walls; prevents oxidation of the metal at the top level of the metal surface in the mold; and usually adheres to the congealed metal where it emerges from the mold thus preventing excessive oxidation at that zone.

A disadvantage of the use of a blanket of glass-like or molten salt material as defined above resides in the gas generating content of suitable glass-like or molten salt materials such as borax and borax glass which may contain undesirable amounts of gas. Other suitable glasses for the purpose of this invention typically may have 50 to 100 cc. of gas per 100 grams of glass.

Borax and borax glasses may have undesirable amounts of contained moisture leading to undesirable turbulence if used in a glass blanket as taught in this invention. For instance, anhydrous borate, B 0 may have one half percent of water, boric acid, B O -H O, may have 44 percent water, borax, NEI2B407, may have one half percent of water, and borax glass may have 50 milliliters of gas per 100 grams.

It is well known that hydrogen dissolves atomically in both solid and liquid iron and because only atomic hydrogen dissolves in steel, the dissociated portion of the hydrogen atmosphere controls the solubility. This dissociation of water into hydrogen and oxygen and of the 3,318,363 Patented May 9, 1967 "ice hydrogen into atmospheric hydrogen increases markedly with the temperature and, therefore, any moisture content in the glass-like or molten salt material utilized in placing a blanket on the pool of molten metal in the continuous casting mold becomes very deleterious to the steel being cast. It has been determined that as small an amount as about 1.5 parts per million of hydrogen is about all that can be tolerated in steel if hydrogen brittleness is to be held to a commercially desirable limit. Flaking on forgings due to hydrogen is dependent upon section size. In thin sections the problem is not difiicult, but shafting requires that the hydrogen be held to an upper limit of about 1.5 parts per million. Indicating how a very small amount of hydrogen may cause damage to steel, the normal humidity in the air has such a great eflect on hydrogen-caused defects in steel, that when melted under atmospheric conditions entailing only natural humidities, hydrogen potentials are developed to such an extent that the difference is often noted between steel made in summer and that made in winter. This hydrogen solubility in steel is greatly pronounced at the higher temperatures as may be noted from the steep solubility curve for hydrogen in liquid steel and the pronounced isothermal change at the solidification temperature. Hydrogen brittleness causes lack of workability and ductility in the steel, less reduction per drawing die, a less number of reductions between annealings, more cracking during cold upsetting, and other undesirable results when working the steel.

Therefore, an object of the present invention is the preheating of glass-like or molten salt material before using it as a blanket layer on top of metal in a continuous casting mold to a temperature and for a period of time sufiicient to substantially dehydrate and degas the glass-like or molten salt material.

The drawing shows a fragme'ntal sectional view, greatly reduced in size, through a continuous casting mold showing the congealing metal passing through the mold with a blanket of glass-like or molten salt material protecting the top of the metal in the mold and flowing into the air gap between the congealing metal and the mold walls, such gap being enlarged in the drawing for clarity.

At 10 I have shown a portion of a cooled mold suitable for carrying out this invention, although it will be understood that any cooled continuous casting mold may be utilized. The mold has an open through passageway from top to bottom which may have any desired cross section. The walls of the passageway are uninterrupted and are open only at the top and bottom for the introduction of molten metal at the top and the substantially continuous withdrawal of a congealed or partially congealed metal bar at the bottom of the mold. Usually the mold is provided with hollow walls which are provided with a cooling fluid such as Water in the chambers 11. The molten metal is introduced in a stream 12 at the top of the mold and is as here shown coming from a tundish 13 although it may be poured directly from a ladle or other container. Means is provided for introducing degassed and dehydrated glass-like or molten salt material of this invention at 14 on top of the molten pool M in the mold. In the present instance, an open chute or duct 15 is provided for this purpose. This blanket of fluid glass-like or molten salt material forms a meniscus at 16 where it is in contact with the mold through passageway 17. As the molten metal at the top of the mold first strikes the cooled Walls 10 of the through passageway '17, a thin skin begins to congeal on the metal as indicated at 18. It should be understood that the blanket of glass-like or molten salt material near 18 is greatly exaggerated in thickness as shown in the drawing because actually the air gap at this point is very small but the glass-like or molten salt material has entered down into the air gap and the metal congeals against the glass-like or molten salt material rather than directly against the mold wall itself. As the metal passes downwardly in the mold, the shell of congealing metal greatly thickens in extent as indicated at 19 and the layer of glass-like or molten salt material settles down to a rather thin shell as indicated at 20 which fills what would otherwise be an air gap between the metal and the mold passageway, thereby performing the functions of increasing heat transfer between the metal and the mold wall 10, lubricating the passage of the metal through the passageway 17, and protecting the walls of the passageway against damage.

Those familiar with this art will understand that a metal bar either congealed or sutficiently congealed to hold together emerges susbtantially continuously from the lower end of the passageway 17 at a guided and controlled rate under the influence of pinch rolls not shown here.

Also, it is quite common to play a water stream on the discharging metal bar so as to further cool the same. These additional facilities for handling the congealed metal :form no part of the present invention and, therefore, need not be shown here.

The glass-like or molten salt materials which'may be used in carrying out this invention include borax; window glass; bottle glass; sodium silicate glass Na O, 33.34%, SiO 65.4%, and small amounts of other oxides mostly of aluminum, iron, calcium and magnesium; potassium silicate glass K 0, 27.84%, SiO 70.75%, and small amountsof other oxides mostly of aluminum, iron, calcium and magnesium. The phosphate glasses also may be used, The viscosity of the glass or salt should not be over 100 poises at the point of use, usually at a temperature between 1500 F. and 2800 F.

If the viscosity of the glass-like or molten salt material is too high for use as taught herein, such viscosity may be reduced by adding small amounts of K or CaF or in some cases A1 0 Some of the glass-like or molten salt materials may have a proper viscosity but the surface tension may be a little too high. In that case small amounts of boric oxide will reduce the surface tension.

In order to dehydrate the glass-like or molten salt mate- 7 rial of this invention, it should be first heated to a very fluid condition which will be approximately 2350" F. or even higher. For instance, for use with about 100 tons of steel, no more than 2000 pounds ofglass-like or molten salt blanket material would be necessary, Such a volume of glass or saltis heated to between 2800 and 2900 F.

and held there until the gas content is reduced to an acceptable level so that it is suitable for use as taught in the present invention. Preferably, the glass-like or molten salt material in such a fluid condition will be introduced on top of the metal in the mold as indicated at 14 in the drawings.

One of the advantages of this invention is that when the glass-like or molten salt material is dehydrated and degassed before using it as a blanket or layer on top of the molten steel, turbulence, due to the presence of gaseous material being driven off the glass-like or molten salt material, is avoided at the point where the molten metal is congealing against the walls of the mold. This reduces the chance of inclusions of slag-like material in the surface of the metal cast.

During the continuous casting of metals, it is well known that the slag in the metal is rejected during solidification, forming a scum layer continuously on top of the metal in the mold. As this layer accumulates, the slag ruptures and surface defects in the metal as cast. To prevent this, the present invention proposes to feed continuously to the mold, and into the slag scum layer on top of the molten metal, a flux such as the degassed glass-like or molten salt material hereinabove described, so as to join with the slag rejected from the metal to produce a fluid blanket capable of acting as a lubricant between the metal and the mold wall as the metal travels downwardly in the mold during the congealing action The glass-like or molten salt material of this invention is, therefore, fed continuously as required to the layer on top of the molten metal in the mold to continuously reduce the viscosity of the layer floating on the molten steel and holding the same preferably to a viscosity of poises or under. This will form a lubricant as indicated at 20 in the drawing preventing the formation of cold shuts, surface defects and fissures in the. metal'as cast.

What is claimed is:

1. In the method of continuously casting metal by passing molten metal into the top of a mold having walls at a temperature which will congeal metal and having an open-top passageway and continuously withdrawing the bar of at least partially congealed metal at the bottom of the mold by substantially continuous relative movement between the metal and mold walls, and wherein there is maintained on top of the molten metal in the mold and in direct contact with the metal, a layer of substantially liquid glass-like or molten salt material having a high fluidity below the melting point of the metal being cast, and wherein the sole heat supplied in the mold other than from the glass-like or molten salt layer is obtained from the metal being cast; the novel step of preheating the glasslike or molten salt material before using it in said layer, to a temperature and for a period of time sufficient to substantially degas said glass-like or molten salt material.

2. In the method of continuously casting metal by passing molten metal into the top of a mold having walls at a temperature which will congeal metal and having an open top passageway and continuously withdrawing the bar of at least partially congealed metal at the bottom of the mold by substantially continuous relative movement between the metal and mold walls, and wherein the sole heat supplied in the mold other than from the glass-like or molten salt layer is obtained from the metal being cast, and wherein there is maintained on top of the molten metal in the mold and in direct contact with the metal, a layer of substantially liquid glass-like or molten salt material having a high fluidity below the melting point of the metal being cast; the novel step of preheating the glass-like or molten salt material before using it in said layer, to a temperature and for a period of time sufficient to substantially dehydrate and substantially degas said glass-like or molten salt material.

3. The method as defined in claim 1 wherein said novel step includes a material chosen from the group consisting of borax, window glass, bottle glass, sodium silicate glass, phosphate glasses and potassium silicate glass.

4. The method as defined in claim 1 wherein said novel step includes heating said glass-like or molten salt material to at least approximately 2350 F. and holding the same at that temperature for at least approximately four minutes.

5. The method of lubricating the pas-sage of metal through a continuous casting mold wherein molten metal is poured into the top of an open mold passageway and at least partially solidified metal is withdrawn through the bottom of said passageway, comprising degassing a glass-like or molten salt material chosen from the group consisting of borax and glasses having a viscosity under about 100 poises between 1500" F. and 2800 F., and feeding said material between said metal and the adjacent walls of said mold forming said passageway.

6. In the method of continuously casting metal by passing molten metal into the top of a mold having walls at a temperature which will congeal metal and having an 5 6 open-top passageway and continuously withdrawing the References Cited by the Examiner bar of at least partially congealed metal at the bottom of UNITED STATES PATENTS the mold by substantially continuous relative movement between the metal and mold walls and wherein a scum 2,369,233 2/1945 Hopkins layer of slag accumulates on the surface of the metal in 5 2,825,947 3/1958 G035 3,151,366 10/1964 Fromson Z257.2

the mold; the novel step of adding to said layer during Sung l T' degasseq glass'llke J. SPENCER OVERHOLSER, Primary Examiner. molten salt matenal to mamtaln the vrscoslty of sad laver below approximately 100 poises. R. S. ANNEAR, Assistant Examzner. 

1. IN THE METHOD OF CONTINUOUSLY CASTING METAL BY PASSING MOLTEN METAL INTO THE TOP OF A MOLD HAVING WALLS AT A TEMPERATURE WHICH WILL CONGEAL METAL AND HAVING AN OPEN-TOP PASSAGEWAY AND CONTINUOUSLY WITHDRAWING THE BAR OF AT LEAST PARTIALLY CONGEALED METAL AT THE BOTTOM OF THE MOLD BY SUBSTANTIALLY CONTINUOUS RELATIVE MOVEMENT BETWEEN THE METAL AND MOLD WALLS, AND WHEREIN THERE IS MAINTAINED ON TOP OF THE MOLTEN METAL IN THE MOLD AND IN DIRECT CONTACT WITH THE METAL, A LAYER OF SUBSTANTIALLY LIQUID GLASS-LIKE OR MOLTEN SALT MATERIAL HAVING A HIGH FLUIDITY 